MOLLUSCA. 265 



less. The following interesting observations were commuLi- 

 cated by Mr. Warrington, in the tenth volume of the ' Annals 

 of Natural History.'' " These Water-Snails have the extra- 

 ordinary power of moving along the surface of the water 

 with great rapidity, with their shells downwards, the foot 

 being attached as it were to the atmospheric air. The I*la- 

 norhis also can lix itself, without any apparent means of 

 attachment, by his side to the flat surface of the glass, and 

 will remain thus for several days. 



" In watching the movements of the Limncece, I was for 

 some time under the impression that they had a power of 

 swimming or sustaining themselves in the water ; as they 

 would rise from the bottom of the pond, a portion of the 

 rockwork, or a leaf of the plants, and float for a consider- 

 able period, nearly out of their shells, without any apparent 

 attachment, and, by the contortion and gyration of their 

 body and shell, move some Kttle distance in a horizontal 

 direction from the point which they had left. On more 

 carefully watching this phenomenon however, I found they 

 were attached by a thread or web, which was so transparent 

 as to be invisible, and wliicji they could elongate in a similar 

 way to the Spider; they also possessed the power of re- 

 turning upon this tliread by gathering it up as it were, 



